The present invention relates to a hydraulic control system for an automatic transmission. More particularly, the present invention relates to a hydraulic control system for an automatic transmission in which the hydraulic control system is capable of operating a powertrain having five forward speeds.
An automatic transmission for vehicles generally includes a torque converter; a powertrain, which is a multi-stage gearshift mechanism connected to the torque converter; and a hydraulic control system for selecting one of a plurality of operational elements of the powertrain depending on driving and load conditions.
Among these main elements of the automatic transmission, the hydraulic control system, which concerns the present invention, includes a pressure regulator for regulating hydraulic pressure generated by the operation of a hydraulic pump, a manual and automatic shift controller for forming a shift mode, a hydraulic pressure controller for regulating shift feel and responsiveness to form a smooth shift mode during shifting, a damper clutch controller for controlling operation of a damper clutch in the torque converter, and a line converter for varying the flow of hydraulic pressure through a plurality of lines such that a suitable hydraulic pressure is supplied to each friction element.
In the automatic transmission with the above elements, hydraulic pressure is varied and line conversion is performed by solenoid valves that are ON/OFF-controlled and solenoid valves that are duty-controlled by the hydraulic control system such that hydraulic pressure is supplied to the correct friction element(s) to realize shifting into the desired shift speed.
Although the powertrain and hydraulic control system are configured and developed differently depending on the manufacturer, the 4-speed automatic transmission is the most common type of automatic transmission used by automakers.
However, the limited number of speeds of the 4-speed automatic transmission (compared to, for example, a 5-speed transmission) is such that there is a significant dissimilarity in gear ratios between the different speeds. This increases fuel consumption. Further, with the increasing emphasis on performance and drivability, such a difference in gear ratios and the limited number of speeds make the 4-speed automatic transmission an unattractive alternative to the 5-speed automatic transmission.
The present invention provides a hydraulic control system for better control of a powertrain in a 5-speed automatic transmission. In preferred embodiments, the system is adapted to control a transmission including five clutches and three brakes to minimize fuel consumption and more efficiently use engine torque. In one embodiment, a manual valve is indexed with a driver-operated shift selector to undergo port conversion. A first pressure control valve is controlled by control pressure of a first solenoid valve. The first pressure control valve preferably supplies N range pressure from the manual valve selectively to a fifth clutch in fourth and fifth speeds, and to a first brake in the neutral N range and the low L range. A second pressure control valve is controlled by control pressure of a second solenoid valve. The second pressure control valve supplies D range pressure from the manual valve selectively to a second brake in the second speed and the fifth speed; and, simultaneously, as control pressure of a first fail-safe valve. A third pressure control valve is controlled by control pressure of a third solenoid valve. The third pressure control valve supplies D range pressure from the manual valve to a first clutch in the first speed, and to a fourth clutch in the low L range and in second, third, and fourth speeds. A fourth pressure control valve is controlled by control pressure of a fourth solenoid valve. The fourth pressure control valve supplies line pressure as control pressure for a third brake and the third solenoid valve in first, second, and third speeds, and in the reverse R range and the neutral N range.
A number of switching valves are also preferably provided. A first switching valve switches hydraulic ports (i.e., port conversion) to selectively supply D range pressure, first pressure control valve pressure, and line pressure to the first clutch and to the fourth clutch. The fourth clutch operates in the first, second, third, and fourth speeds and in the reverse R and low L ranges. A second switching valve, controlled by L range pressure, D range pressure, and control pressure of the fifth solenoid valve, selectively supplies hydraulic pressure to the first pressure control valve to a second clutch and the first brake, which operate in the third, fourth, and fifth speeds. A fifth solenoid valve controls pressure from a reducing valve to selectively supply the pressure as control pressure to the first and second switching valves. A third switching valve, controlled by line pressure and second clutch pressure, selectively supplies hydraulic pressure supplied from the second switching valve to the second clutch and the fifth clutch. A N-R control valve, controlled by control pressure of the second solenoid valve, supplies R range pressure from the manual valve to a third clutch in the reverse R range.
The first fail-safe valve is controlled by line pressure, second brake pressure, and second clutch pressure, and selectively supplies hydraulic pressure from the manual valve and the second switching valve to the first brake. The first fail-safe valve prevents simultaneous engagement of the first and second brakes, and prevents forward driving by engagement of the first brake and the second clutch when in the neutral N range. A second fail-safe valve is controlled by R range pressure, second and fourth clutch pressure, and N range pressure. The second fail-safe valve prevents simultaneous engagement of the second brake and the first, second, and fourth clutches, and selectively supplies hydraulic pressure from the second pressure control valve to the second brake. A third fail-safe valve is controlled by D range pressure and third brake pressure, and selectively supplies hydraulic pressure from the third switching valve to the fifth clutch. The third fail-safe valve prevents the simultaneous operation of the third brake and the fifth clutch.